It seems the LEGO have ceased to sell the straight and curved shaped tracks separately (for the time being, anyway) which is a big shame. It was unfortunate enough when they discontinued 9V compatible rails/motors in 2007, but to merge all available track parts into one package is only going limit creative potential. I imagine this move has only been taken for cost reasons, as was the case with the 9V situation.
The included 'Flexible Tracks have good and bad pointers. On the upside, they full-fill something that has been longed for for years; the ability to shape track layouts in a more natural way, which is particularly nice when you're working in a tight environment. But these are no good if you drive the trains too fast, for they simply slip off the rails.
So... Strange situation at the moment with LEGO trains. Whilst I appreciate that these plastic tracks are generally cheaper than products that preceded it, I am now buying from ME Models (online store) who provide a D.I.Y kit for tracks, allowing one to build their layout through separate rail and sleeper components. Compatible with both Power Functions and 9V trains, too!